ATP1A3 and alternating hemiplegia of childhood: AHC (OMIM 614820) is an infantile-onset (<18 months) and the most common ATP1A3-related disorder, with a reported prevalence of between 1 in 1,000,000 (Neville and Ninian, 2007) and 1 in 100,000 children (Hoei-Hansen et al., 2014).